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\begin{document}

\mainmatter              % start of the contributions
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\title{A relational algebra for temporal databases}
%\title{Introducing valid time in bipolar database querying}
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%\titlerunning{A Fuzzy Valid-Time Model}  % abbreviated title (for running head)
%                                     also used for the TOC unless
%                                     \toctitle is used
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\author{Jose Enrique Pons\inst{1} \and Christophe Billiet\inst{2} \and Guy De Tr\'e\inst{2} \and Olga Pons Capote\inst{1} }

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%\authorrunning{Ivar Ekeland et al.} % abbreviated author list (for running head)
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%%%% list of authors for the TOC (use if author list has to be modified)
%\tocauthor{Ivar Ekeland, Roger Temam, Jeffrey Dean, David Grove,
%Craig Chambers, Kim B. Bruce, and Elisa Bertino}
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\institute{Department of Computer Science and Artificial Intelligence \\
University of Granada \\
C/Periodista Daniel Saucedo Aranda s/n E-18071 (Granada-Spain) \\
\email{jpons,opc@decsai.ugr.es}\\ 
%WWW home page:
%\texttt{http://users/\homedir iekeland/web/welcome.html}
%\and
%Universit\'{e} de Paris-Sud,
%Laboratoire d'Analyse Num\'{e}rique, B\^{a}timent 425,\\
%F-91405 Orsay Cedex, France
\and 
Department of Telecommunications and Information Processing,\\
Ghent University,\\
Sint-Pietersnieuwstraat 41, B-9000 Ghent, Belgium\\
\email{Christophe.Billiet,Guy.DeTre@UGent.be}
}

\maketitle              % typeset the title of the contribution

\begin{abstract}

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\end{abstract}

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\section{Introduction}

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\input{intro}

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\section{\label{sec:preliminaries}Preliminaries}
The basics on possibility theory is introduced within the first subsection. Then, some background concepts about temporal databases are introduced. Finally, the representation of imperfect temporal intervals is explained.
\input{possibilistic}
\subsection{Time in databases}
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\input{time}

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\section{\label{sec:proposal}Algebra for crisp temporal databases}
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\input{temporal-model.tex}

\input{crisp-algebra.tex}

\section{Algebra for (fuzzy) temporal databases}
\input{fuzzy-model.tex}
\input{fuzzy-select.tex}

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\section{\label{sec:conc}Conclusions}
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%\input{conclusions}
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\subsubsection{Acknowledgements}
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\input{acknowledgements}



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